Epidermal growth factor (EGF) is a polypeptide hormone which is mitogenic for epidermal and epithelial cells. When EGF interacts with sensitive cells, it binds to membrane receptors; the receptor EGF complexes cluster and then are internalized in endocytotic vesicles. This is responsible for the phenomenon of "down-regulation". EGF binding induces a tyrosine kinase activity of the receptor molecule and induces synthesis of DNA.
The EGF-receptor is a transmembrane glycoprotein of about 170,000 Daltons. (Cohen, J. Biol. Chem., Vol. 258, pp. 1523-1531, 1982.) It is the gene product of the c-erb-B proto-oncogene. (Downward, et al., Nature, Vol. 307, pp. 521-527, 1984.) The receptor exists in two kinetic forms: so-called, low affinity and high-affinity receptors. These may be interconvertible. (Fernandez-Pol, Biol. Chem., Vol. 260, pp. 5003-5011, 1985.)
The A431 carcinoma cell line expresses abundant EGF-receptors on its cell surfaces, and thus has been used in many studies to generate anti-EGF-receptor antibodies. However, the receptors on A431 differ from those of other cell types in the carbohydrate moieties attached to the polypeptide. Thus many antibodies raised against A431 membranes are directed against carbohydrates which are not common to all forms of the receptor molecule. (See, for example, Richert, Fed. Proc., Vol. 42, p. 1094, 1983, Schreiber, J. Biol. Chem., Vol. 258, pp. 846-853, 1983, Gooi, Bioscience Reports, Vol. 3, pp. 1045-1052, 1983, Vol. 5, pp. 83-94, 1985 and Molecular Immunology, Vol. 22, pp. 689-693, 1985.)
Others have generated monoclonal antibodies which are reactive with the protein moiety of EGF-receptors. These antibodies display a variety of properties upon binding to EGF-receptors, presumably dependent on the particular portion of the receptor molecule bound, and the isotype of the antibody. Some antibodies mimic some of the effects of EGF (agonists) and some inhibit the effects (antagonists).
Expression of EGF-receptors has been implicated in the progression of tumor growth. The gene for the receptors has been found to be the cellular analogue of the arian vital oncogene v-erb-B. (Ullrich, et al, Nature, Vol. 309, pp. 418-425, 1984.) In addition, an association has been detected between late stages of melanoma development and extra copies of the chromosome carrying the receptor gene. (Koprowski, et al., Somatic Cell and Molecular Genetics, Vol. 11, pp. 297-302, 1985.)
Because EGF receptors are expressed on a wide variety of solid tumors they provide a suitable target for anti-tumor therapy. However, there is a need in the art for a suitable anti-receptor antibody. Many of the known antibodies have properties which would be deleterious if used as anti-tumor agents. For example, antibodies which mimic the effects of EGF could stimulate the progression of the tumor rather than arresting it. Other antibodies which only bind to high or low affinity receptors could be less than optimally effective because EGF could still exert its effect through the unbound receptors. Still other antibodies convert low affinity receptors to high affinity receptors, which could exacerbate tumor growth rather than inhibiting it. Thus there is a need in the art for an anti-EGF-receptor antibody which would be suitable for anti-tumor therapy.